Pressure sensors have become ubiquitous the last several years, finding their way into many applications, such as tire pressure monitor systems (TPMS), manifold absolute pressure (MAP) applications for example in automotive exhaust lines, automatic transmission gear boxes, consumer applications involving barometric pressure measurements, and others.
These pressure sensors are typically formed on a silicon die having a diaphragm over a cavity, where the diaphragm is supported by a sidewall or bulk region. One or more sensors, such as a Wheatstone bridge consisting of diffused or implanted resistors, are located on the diaphragm. Pressure, either from above the diaphragm or below in a cavity, deflects the diaphragm and its sensors. This deflection, and hence the pressure, can be measured by utilizing the piezo-resistive effect. That is, as the sensors are stressed due to the bending of the diaphragm, the piezo-resistive effect changes the value of one or more of the resistors that are typically configured in the Wheatstone bridge. This change in resistance results in a change in the output of the Wheatstone bridge from which the change in pressure can be inferred.
Pressure sensors are typically placed in a package or other housing. The package or housing enables the electrical connectivity and protects the pressure sensors against its environment. For example, they may be fixed to a surface and partially covered in plastic. This packing often tends to stretch or compress the pressure sensor die. This in turn induces stress on the device's diaphragm. This stress may be indistinguishable from the pressure that the device is intended to measure, and it may create offsets and other errors in the pressure sensor output. While the effects of this stress may be initially removed by the calibration of the device, the stress may change over time and temperature, with this change in stress appearing as a change in the output of the pressure sensor.
Thus, what is needed are circuits, methods, and systems that calibrate or account for these variable packaging and related stress components. In order to accurately account for this, it is further desirable to have available an improved sensor element or device to use in place of the simple Wheatstone bridge.